Pouched Lamprey

The pouched lamprey (Geotria australis) is one of only a handful of lamprey species found in the Southern Hemisphere, occurring around southern Australia, Tasmania, New Zealand, and the southern tip of South America. As a member of the ancient jawless fish order Petromyzontiformes, it lacks true jaws, paired fins, and a bony skeleton, instead using a circular, toothed sucking disc to attach to host fish during its parasitic ocean phase. Its common name comes from a distinctive fleshy pouch that forms under the throat of breeding males, a feature not shared by other lamprey species worldwide. Like other lampreys, it is anadromous, spawning once in freshwater rivers before dying, and its larvae spend years buried in river sediment before transforming into adults.

• Long, scaleless, eel-like body; silvery-blue at sea, becoming golden-bronze in fresh water
• Circular sucker-disc mouth lined with concentric rows of small horny teeth
• Seven round gill openings on each side of the head
• A single continuous or notched dorsal fin positioned toward the tail
• Breeding males show a loose, baggy pouch beneath the throat, the species' defining field mark

This throat pouch is unique among lampreys and is the most reliable way to distinguish breeding male pouched lampreys from the similarly sized short-headed lamprey, which has a shorter head and no pouch.

Pouched lampreys are anadromous, with adults spending roughly one to two years feeding in open coastal waters of the cool temperate Southern Hemisphere before entering rivers to breed. Their range spans southern Australia, Tasmania, New Zealand, and parts of southern South America, making them one of the most widely distributed lamprey species in the region. During the freshwater phase, adults migrate upstream through rivers and streams to gravel-bottomed spawning areas, while ammocoete larvae burrow into silty or sandy substrate in slower sections of the same rivers for several years. Free passage between ocean and river habitat is essential to their life cycle, and dams or weirs can block their migration.

At sea, pouched lampreys are parasitic, using their sucking disc mouth to latch onto other fish and feed on blood and tissue fluid. Once they begin their spawning migration into rivers, adults stop feeding altogether and rely entirely on stored fat reserves, with breeding males developing their characteristic throat pouch during this period. After building simple gravel nests and spawning, adults die shortly afterward. The burrowing ammocoete larvae that hatch from the eggs are filter feeders, straining detritus, algae, and microorganisms from river sediment for several years before metamorphosing into the free-swimming adult form. This dual marine-freshwater life history links ocean and river ecosystems across its Southern Hemisphere range.